1. Field of the Invention
The invention relates to graft copolymer polyols for use in the production of polyurethane polymers. In particular, the present invention relates to novel graft copolymer polyols prepared by reacting an ethylenically unsaturated monomer in the presence of a polyol compound containing an azo linkage, and to the use of these polymer polyols in the production of polyurethanes.
2. Prior Art
A great deal of art has arisen focusing on methods for increasing the overall molecular weight of polyols without seriously affecting chain length and attendant fluidity, by incorporating polymeric materials onto the polyol by grafting. Such grafted copolymer polyol dispersions have proven to be advantageous when used in polyurethane formulations to achieve desirable polyurethane product properties, such as enhanced load bearing and resiliency in foams.
It is known in the art to prepare graft copolymer dispersions from vinyl monomers and polyols and to use these copolymers in the formulation of urethane polymers. For example, U.S. Pat. No. 3,383,351 to Stamberger teaches that ethylenically unsaturated monomers may be polymerized in a polyol medium. As evidenced by Pizzini et al in U.S. Pat. No. 3,823,201, graft copolymers could also be formed by reacting vinyl monomers in polyols containing some degree of unsaturation. An effective amount of free radical catalyst is required in order to initiate these copolymerization reactions. Such free radical-type vinyl polymerization catalysts are, for example, the peroxides, persulfates, perborates, and azo compounds, etc.
It is also known in the art to prepare graft copolymers by treating polymerizable vinyl-type monomers with azo-containing polymers. This is illustrated in U.S. Pat. No. 3,752,802 to Sheppard et al, which shows (see Example X) the preparation of such azo compounds by reaction of an azo-bis diacid chloride, such as trans-4,4'-azobis-(4-cyanovaleryl chloride), with a monohydroxyl-terminated polyether. The prepared azo-containing polymers are reacted with suitable vinyl monomers under conditions where the azo-carbon linkage is decomposed into free radicals at a rate and temperature suitable for polymerizing the vinyl monomer. These graft copolymers are suggested to have utility as stabilizers of solutions of different homopolymers. However, the azo-containing polymers illustrated are not azo di-ester polyols and accordingly do not feature the multiple hydroxyl groups as are necessary for graft copolymers for use in polyurethane formulations; the basic chemistry of polyurethanes is the reaction of a polyfunctional material that has multiple terminal hydroxyl groups with a polyisocyanate to render a product of high molecular weight. The amount of branching and cross-linking of the polymeric product is directly dependent on the number of hydroxyl groups in the original material. By altering the amount of hydroxyl groups, the physical properties of the resulting polyurethane can be varied to form products such as elastic fibers, elastomers, or flexible, semi-rigid, or rigid foams.